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Old 10-15-2005, 01:41   #1 (permalink)
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short shifting autos

I noticed question in another post re: revving cleveland to 6200 on gearchanges.
Has anyone been happy with, say 6500 rpm shifts (at drags) and then started short shifting maybe even as far back as approx 5700 rpm?

What results did you get i.e. et wise? What happened to the speed?
Did car run quicker et's but feel slower or felt slow and ran slow et's?

Cheers Northey
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Old 10-15-2005, 02:49   #2 (permalink)
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Re: short shifting autos

Quote:
Originally Posted by northey
I noticed question in another post re: revving cleveland to 6200 on gearchanges.
Has anyone been happy with, say 6500 rpm shifts (at drags) and then started short shifting maybe even as far back as approx 5700 rpm?

What results did you get i.e. et wise? What happened to the speed?
Did car run quicker et's but feel slower or felt slow and ran slow et's?

Cheers Northey

I assume your referring to my post.....mate it will depend on the car and the set-up !! You need to compare apples with apples..ie... a clevo with a big solid cam and high stall won't be anything like a mild hydro cam and a average stall.
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Old 10-15-2005, 03:12   #3 (permalink)
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Re: short shifting autos

It was your post that triggered my question but isn't anything to do with your setup or my own rebuild.

Just curious as to who's tried it and what results they got in any type of cleveland.
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Old 10-15-2005, 03:18   #4 (permalink)
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Re: short shifting autos

Well in mine i was changing at 7500rpm then 6700 rpm i went 6 tenths faster at lower revs but the mph was the same.
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Old 10-15-2005, 03:25   #5 (permalink)
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Re: short shifting autos

I shift at 6,500 1-2 then 6,500 2-3 and go across the line at 7,400. 140mph. Goes slower if i rev it harder.
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Old 10-15-2005, 16:56   #6 (permalink)
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Re: short shifting autos

I shift at 6200rpm more than that I get a loud valve float noise!
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Old 10-15-2005, 17:39   #7 (permalink)
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Re: short shifting autos

At the track, i changed my shift from 6200rpm up to 6900 rpm and
picked up 2 tenths. Oviously its a trial and error thing for each and every combo.
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Old 10-16-2005, 01:27   #8 (permalink)
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Re: short shifting autos

I don't mean to sound ignorant guys & please correct me - (1/4 mile bunny)
Isn't the idea to shift at or close to where the engine makes max torque for optimum acceleration???
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Old 10-16-2005, 01:55   #9 (permalink)
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Re: short shifting autos

Quote:
Originally Posted by Tones Teo
I don't mean to sound ignorant guys & please correct me - (1/4 mile bunny)
Isn't the idea to shift at or close to where the engine makes max torque for optimum acceleration???

The general idea is to shift just beyond peak torque to the degree that the engine loses the minimum amount of RPM (RPM drop is lowest) through the gear change.

On a gear change, the engine will drop RPM. That's expected. What we want to do is relocate the RPM in the band where it will continue to pull strongest. Most vehicles use a fairly wide ratio transmission. This ensures that there will be a significant RPM drop on every gear change, whether manual or auto.

The killer thing for us is to have a six speed instantly shifting automatic transmission that keeps the RPM rise and fall to about 1000 RPM right in our peak torque band...but that isn't very practical, affordable or even reasonably feasible...is it? So we use camshafts, tire sizes, differential gears and stall converters to give us the strongest possible lauch and top speed for the RPM range that our engines have once built.

The engine dyno, even a "Desktop" dyno will tell us the effective RPM band for an engine with detailed information about that engine. Chassis dynos will show us where our engine pulls in our particular combination and what RPM band it favors. There is some potential benefit by slightly exceeding the top end of that band during gear changes, but certainly not to the point of floating the valves, which is always a no-no.

The bottom line tends to be what works best at the track versus what sounds good on paper. As every combination is different, it is unlikely that there is an easy answer to the question without some simple hardware.

Basically, what you want to do in the car to really test the most effective gear change RPM is to use an accelerometer with feedback. Once your acceleration rate increase drops, you want to change gears.


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Old 10-16-2005, 22:58   #10 (permalink)
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Re: short shifting autos

davis wait until they suss out how to up the line pressure on the new ZF 6 speed auto's in our falcons over here...
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